In medical radiography such as X-ray photography, a "both-sided emulsion film type" silver halide photographic material (in which a photosensitive silver halide emulsion layer is provided on either side of a transparent support) is used and two radiographic intensifying screens are placed on both of the front and the back sides of the photographic material. A combination of the photographic material and the radiographic intensifying screens are then exposed to X-rays having passed through a patient. Such "both-sided photographic film system" is generally employed to obtain a radiation image of high quality with high sensitivity. However, the sharpness of the resultant image is often lowered by "cross-over light". The term of "cross-over light" means a visible light emitted by the radiographic intensifying screens which are placed on each side of the photographic material and then passes through the support of the photographic material to reach the photosensitive layer provided on the opposite side to deteriorate the sharpness. The deterioration thus caused by the cross-over light is referred to as "cross-over phenomenon".
In order to reduce the cross-over light (hereinafter, often referred to as simply "cross-over"), various studies on a silver halide photographic material (herenafter often referred to as "photographic material" or "photosensitive material") and a radiographic intensifying screen (hereinafter often referred to as "intensifying scree" or "screen") have been made.
As the studies on the photographic material, for example, Japanese Patent Provisional Publications No. H1-166031 and No. H1-172828 disclose a method using a mordant polymer and a method using a solid fine crystalline dye, respectively. In those methods, however, a considerably large amount of dye should be incorporated into the photographic material so as to satisfactorily reduce the cross-over light. Such large amount of dye is hardly removed rapidly in a development treatment. Therefore, into practically employable photographic materials, such large amount of dye cannot be incorporated. Further, if the dye is used in a large amount, an intensifying screen is liable to be stained with the dye transferred from the photographic material because the dye is insufficiently fixed to the photographic material. Although various dyes have been proposed to solve this problem, a satisfactory dye still has not been reported.
A method using an intensifying screen which can intercept the cross-over light is also proposed in, for example, WO 93-01521, EP 650089 and EP 592724. In the method, luminescence of phosphor is shifted to the ultraviolet region so as to reduce the cross-over light.
With respect to an intensifying screen containing Gd.sub.2 O.sub.2 S:Tb phosphor, various proposals are reported. Japanese Patent Provisional Publication No. 61-151534 discloses an intensifying screen in which a light-absorbing dye is contained and the phosphor is chosen so that a light emitted by the intensifying screen may comprise a green light component more than a blue light component. Each of Japanese Patent Provisional Publications No. 62-222200 and No. H4-155297 discloses a screen having differently colored phosphor layer to give an image of improved sharpness. RD83-22709 and RD82-218041 suggest that the sharpness of a resultant image can be improved by using a yellow dyesand/or a light-absorbing dye. Japanese Patent Publication No. 58-2640 teaches that the sharpness can be improved by applying a light-absorbing pigment onto the surface of phosphor layer. U.S. Pat. No. 4,362,944 proposes a surface protective layer which absorbs a part of the emitted light. Further, as an intensifying screen giving a low cross-over, an intensifying screen having a yellow-colored phosphor layer is commercially available (Eastman Kodak Co., Lanex Medium [trade name]). However, it appears to be indispensable that the dyes and/or pigments incorporated into an intensifying screen reduce sensitivity.
With respect to an intensifying screen containing a fluorescent dye or pigment, EP 0595089 reports that a phosphor which emits a ultraviolet light improves in corporation with fluorescent dyes the sensitivity. Further, DE 2807398 and DE 3143810 disclose intensifying screens using s fluorescent pigment in the form of fine particles.
Although various studies such as described above have been reported, it seems that there are no studies reporting that the cross-over of radiographic intensifying screens containing rare earth phosphors is well reduced using fluorescent dyes or pigments.
Under the circumstances, a radiation image-forming system giving a radiation image (or radiographic image) of high quality with high sensitivity (i.e., high radiographic speed) is highly desired, and accordingly it is desired to further improve both radiographic intensifying screens and photographic materials.